Telephone-exchange apparatus.



Patented Marqz'd, i900.l

No. 645,57l.

Y c. E. scmnen.

TELEPHONE EXCHANGE APPARATUS.

(Application ledJllovf/G, 1896.)

(No Model.)

co. moin-undo.. msnworon n c UNITED STATES.

PATENT errent CHARLES n. SCRIBNER, or CHICAGO, ILLINOIS, AssieNoIt To 'run WESTERN ELECTRICCOMPANY, or SAME PLACE.

TELEPHONE-EXCHANGE APPARATUS.

SPECIFICATION forming part of Letters Patent No. 645,571, dated March 2o, Ieoo.

Application filed November 16, 1896. ScrialNo. 612,270. (No model.)`

To @ZZ whom, it muy' cotcert:

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illi- 5 nois, have invented a certain new and useful Improvementzin Telephone-Exchange Apparatus, (Case No; 394,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying Io drawing, forming a part of this specification.

My invention concerns the operation of signaling instruments at the central office of telephone-lines, particularly lines provided with means for supplying substation transt5 mitting telephones with Current conveyed from the central office through the line conductor. v

The invention embraces a number of different features, which relate to the charging 2o of a local storage battery over the line conductors, the substation signal-bell, the connections of the return-circuit at the substation, and means for automatically setting a line-signal in the use of the substation-telephone, for effacing that signal in making connection with the line, and for substituting for the line-signal a supervisory signal.

The objects of the several features are to provide a path of low resistance for charging 3o the local battery, to prevent the continuouslyflowing charging current from interfering with the operation of the polarized si glial-bell, to control a subsidiary line-signal through the agency of a relay, to prevent excitement of the relay during the idleness of the line by the charging-current, to render the relay inoperative when connection is made with the line, and to operate a supervisory-lamp signal directly in the circuit of the connected 4o line. 4 In the system constituting this invention the line conductors of a metallic circuit are united at the central ofce andA grounded through the central source of current common to the different lines. The signal-controlling relay, of high resistance, is interposed in one of the line conductors and an impedancecoil of comparatively low resistance is placed in the other line'conductor, both of these in- 5o ductive resistances being located in the lineA line-terminal spring jack or socket.' At.,the substation the line conductors are united through the windings of the' usual polarized signal-bell, of high resistance, and that one 5 5 which contains the impedance-coil is led to ground or other suitable return-conductor through a path in which the local storage battery to be charged is placed. A switch is provided for bringing the telephone appliances 6o into a bridge of the line in the usual Way during the use of the telephone. A branch to the return-conductor is led to the center of the winding of the substation-telephone, a low-resistance impedance-coil being interposed in the conductor to prevent disturbance of the telephonie currents in the line. The

.members ot' the pair of connecting-plugs are united inductively through the windings of a repeating-coil, and a conductor is led from 7o the central point of the winding of the repeating-coil to one pole of the before-mentioned common source of current-supply. In a conductor leading from the source of supply to each of the windings is interposed a supervisory signal-lamp arranged in connection with a local circuit and source of current, whereby the lamp is deprived of current while current exists in the line-circuit, being lighted only When the current in that circuit ceases. 8o

In the normal condition of the line the charging-current tlows over the line conductors jointly and through the return or ground circuit, including the local storage battery at the substation, thus maintaining the charged condition of that battery. Such a large proportion of the current is diverted from the signal-controlling relay in one conductor through the low-resistance impedancecoil in the other line conductor thatthe relay 9o remains inert. For the same reason the substation signal-bell is only very slightly magnetized, so that the operation of the bell by alternating signaling-currents in the line is not hindered by the charging-currrent. The removal of the substation-telephone from its switch-hook for use permits the closing of a connection through a low-resistance circuit from each of the line conductors,whereby the signal-controlling relay is excited and causes roo the display of the corresponding subsidiary line-signal. When connection is made with the line, the relay and impedance-coil become shunted by the low-resistance windings of the repeating-coil in the plug-circuit, assisted by a properly-directed source of current, the relay becoming inert and eiacing the line-signal. Asupervisory-lampsignalissubstituted for the line-signal of each line, which supervisory signal remains undisplayed until at the replacement of the substation-telephone, and the consequent interruption of the current in the line conductors, the source of current in the local circuit about the supervisory lamp causes its illumination. The two supervisory signals associated with the two plugs of the pair have thus the usual function of indicating to the operator the condition of use or disuse of the substation-telephone of the corresponding lines. y

This improved exchange system is illustrated in the drawing herewith. This represents two substations whose lines terminate in a switchboard and pairs of connecting-plugs, with other accessory telephonic signaling and supervisory appliances in the switchboard.

The apparatus at thc substation comprises the usual receiving-telephone a, a transmitting-telephone a', an induction-coil ai', a local storage battery a3, a polarized signal-bell a4, and a telephone-switch o5 for changing the circuit connections when the telephone is brought into use. The winding of the magnet of receiving-telephone a and the secondary winding of induction-coil a2 are divided, portions being included serially in a wire 1, which terminates in normally-open contactpoints of the switch a5. From the point of wire' l intermediate of the winding of the telephone the ground or return circuit of the line is connected, an impedance-coil ct of low resistance-say twenty-five ohms-being included in the ground branch. The switch a5 is constructed with contact-pieces, constituting, respectively, terminals of the line con` ductors 2 and 3, which are closed to the ends of wire l when the switch, relieved of the weight of the telephone, rises. The transmitting-telephone a is contained, together with the primary winding of induction-coil 0,2, in a local circuit 4 of the battery as. This local circuit is controlled also by switch-contacts of switch a5, being closed while the telephone is in use. The bell a4 is connected in a permanent bridge 5 ofthe line conductor and should be of very high resistance, one thousand ohms being suitable resistance. The local battery a3 is included in an earth branch from conductor 3, together with animpedance-coil a7.

The line conductors 2 and are led at the central oftice to the usual spring-jack b and signaling instrument c in a telephone-switchboard and are connected in multiple with a grounded battery d, which serves to excite the signals under certain conditions. The

magnet of the signaling instrument c, which is, in fact, a relay, is included in the line conductor 2. In the other line conductor an im- -tioned.

pedance-coil e is interposed to prevent the shunting of telephonie currents to earth. The relay c controls the subsidiary signalf, preferably a small incandescent lamp, which is included in a local circuit 6, containing a battery g and normally broken atthe switch-contacts of the relay. This signal-lamp f may be associated in the usual way with the springjack or terminal socket l) of the line.

The switchboard is furnished with pairs of connecting-plugs 7L and 7L', whose like parts are united through conductors 7 8 and 9 10, which constitute the plug-circuit, the telephonic connection between conductors 7 and 8 and between conductors 9 and l0 being broken and a repeating-coil t' being interposed in the circuit. The conductors 7 and 9 are, in effect, united through two windings t" and i2 ot' the repeating-coil. The concluetors 8 and 10 are united through other coils 3 and 714, wound upon the same core of the induction-coil.

The usual calling-key 7c is interposed in conductors 8 and l0, leading to the callingplug h for connecting a generator Z of signaling-current into circuit with the plug men- Thereis also a listening-key m, by means of which the operator may connect her telephone lnwith the plug-circuit. Two supervisory signals o and o are associated with a pair of connecting-plugs, one with each.

These signals, which are small incandescent ICO IIO

ferent parts with relation to each other. The

necessary relation will become evident in following the operation of the system; but it may be well to state here the resistances found suitable for the different new appliances. At the substation the impedance-coil a may have a resistance of twenty-five ohms. The bell a4 should be of high resistance-say of one thousand ohms. The impedance-coil a7, in circuit with the local storage battery a3, may have a resistance of tive hundred ohms. At the central office the magnet of relay c may be ot' five hundred ohms, while the iinpedance-coil c would have a resistance not higher than one hundred ohms. The Windings ot' induction-coil t may be of approximately twenty-five ohms each. The resistance-coils q and q may be of ten ohms. Battery el may be of thirty volts, batteryp of ten volts, and battery fr of six or eight volts, depending upon varying conditions of line resistance.

In the normal or idle position of thc ap- 'paratus the current iows from battery d over line conductor 3 and thence to earth at the substation through storage battery c3. The local storage battery is thus continually charged while not in use. A small portion of the current from battery d finds circuit through relay c and bell a4 at the substation; but on account of the high resistance of these instruments the current is not sufficient to operate the relay. The removal of the telephone from the switch at the substation brings the conductor 1 into a bridge of the line, and thus closes a ground branch of comparatively-low resistance to each of the line conductors. The current from battery d through relay c then becomes greatly increased, a circuit being now closed from line conductor 2 through one-half the conductor l to the center of the telephone aand thence to earth through impedance-coil a6, and the relay is magnetized, attracting its armature, and thus causing the illumination of line signal-lamp f. The display of this lamp constitutes a call to the operator, to which she responds by inserting plug h into spring-jack b of the line, whereby she is enabled to bring her telephone into connection with the subscribers line to learn his order. The insertion of the plug into the spring-jack completes a new circuit from battery d to the springjack, including wire ll and conductors? and 9 of the plug-circuit, which lead to the conductors 2 and 3 of the line-circuit, respectively. A local circuit is now formed from wire 11, conductor 9, and a part of the line conductor 2, which includes the winding i2, the relay c, and the battery p. The electromotive force of battery p should be of the proper direction and of such amount in this circuit as to create a condition of no difference of potential between the terminals of the relay with respect to battery d or to approximate such condition. Under that condition the relay c becomes inert and causes the extinction of line-signal f. The current from the batteries d and p iiows out through the two windings i and i2 of the inductioncoil to the substation and through the ground branch there, the circuit being through the conductors 7 and 9 of the plug-circuit to the line conductors 3 and 2, thence to the terminals of the bridge -wire 1, and from that bridge to earth through the impedance-coil c6. A portion ot' this current traverses the supervisory signal o, inasmuch as this lamp is in a branch of the conductor leading to the junction of the coils z" 2,- but so much of the current is diverted from this instrument through the shunt about the lamp by means of battery r that the lamp remains unlighted. It will be understood that the function of battery r is to reduce the difference of potential between the terminals of the lamp in the same way that battery 19 reduces the difference of potential between the terminals of relay c. Thus the act of inserting the plug h into the spring-jack b has brought the operator into communication with the subscriber and has extinguished the line-lamp f and the supervisory lamp o. Having received the subscribers order for the connection required, the operator inserts plug h into the springjack of the desired correspondent line and operates the calling-key 7o to ring the bell at the substation. The efficient operation of the bell by the calling-current thus sent is not impaired by current in the line-circuit from the battery d, as in systems heretofore organized, since this bell receives but a very small proportion of the current flowing in the line for charging the local storage battery d3. The act of inserting plug h' into the springjack of the correspondent line brings supervisory lamp o into a relation to that line similar to that of supervisory lamp o in respect to the calling-line, as before traced. Since, however, there is as yet no complete circuit to earth ot' low resistance at the called substation, the lamp 0 remains still lighted by the current from battery fr, in the closed local circuit of which it forms a part. The battery p, which is connected to ground through the battery d, nds circuit through the winding 4 of the repeating-coil and the strand 10 of the cord-circuit to the sleeve of the plug,

`whence it passes to the thimble of the springjack and to the line conductor 2 ofthe telephone-line. The electromotive force of the battery p and conductor 2 then tends to produce current through the relay c of the called line and back to the other side of the battery through conductor 13, which conductor is that one which connects all the telephone-lines together to grounded battery d. The balance of electromotive force between batteries p and d, the latter having a higher electromotive force, is, however, such that the battery p, while it may tend to reverse the slight current flowing through the relay c from battery d, does not produce sufficient current in this relay to light the signal-lainp'controlled by such relay. Asmall current from battery p may also i'low'out over conductor 2 of the telephone-line to a substation through the signal-bell d4, conductor 4, through the impedancecoil a7 to ground, the return-circuit then being through to earth and back to the other side of the battery 1J through the grounded battery d at the central office. The supervisory signal o' therefore will be lighted by current flowing in the local circuit from battery r until the called subscriber responds--that is, so long as no appreciable current flows from batteries d and p through the plug-circuit. It may be mentioned that during the idle condition of the plugs the supervisory signal-lam ps will be lighted by current from battery r, flowing in their local circuits, and that a supervisory lamp will be extinguished only when the plug with which it is associated is connected with a telephoneline grounded at the substation by the removal of the substation-telephone from its hook. When the subscriber at the called sub- IOO IIO

4 eziavi station removes his telephone from the switch, current is permitted to flow from batteries d and 1J, acting in series through the conductor l2, including the supervisory signal o', and thence to earth at the called substation. The conditions of potential are thus produced in this circuitrequisite for extinguishing the signal-lamp o". The obseuring of this lamp is therefore a signal to the attendant that the called subscriber has responded and has removed his telephone from its switch-hook. When both telephones are thus removed, the apparatus is in position to permit conversation between the subscribers. Telephonie currents created at either substation and {iowing in the circuit made up of the line conductors and aportion of the plug-circuit are induetively propagated or repeated into the other circuit to aect the receiving-telephone therein. When the telephone at either station is replaced on its switch, the current from battery d, through the corresponding supervisory signal and its associated conductors, is interrupted and the supervisory signal becomes excited by current from battery r. The simultaneous lighting of both signals may be accepted by the operator as signifying the termination of conversation, and she may then remove the plugs from their springjacks and return them to their normal positions.

My vinvention is defined in the following claims:

l. The combination with a metallic-'circuit telephone-line. extending from a substation to a central ofce, of a source of current at the central office included in a branch from both limbs of the line in multiple to a returnconductor, a signal-controlling instrument included in one limb of the line at the central office, a local storage battery at the substation included in a branch from the other limb of the line to the return-conductor, and a switch at the substation for controlling the flow of current through the limb which in cludes the signalcontrolling instrumen t, substantially as and for the purpose set forth.

2. The combination with a metallic-circuit telephone-line, of a central source of current in a circuit composed of both limbs of the line in multiple in conjunction with a return-cir in a circuit formed of the line conductors thereof in multiple and a return-conductor, of a signal-controlling instrument and a conductor of high resistance in one of the line conductors, a local storage battery in the other of the line conductors, and a switch at the substation adapted to cut out the said conductor of high resistance, whereby the signal may be operated from the substation, as described.

4. The combination with a telephone-line connected with a source of current at the central oflice, includinga signal-controlling magnet, and provided with a switch controlling the current in the line from the said source, and a'terminal socket of the line, of a plug and cord for making connection with the line, a conductor terminating in the plug` adapted to be brought into shunt of the magnet when the plug is in the socket, and a second source of current in the conductor of proper polarity and strength to produce a condition of no difference of potential between the terminals of the magnet when the said shunt is complete, substantially as described.

5. The combination with a metallic-circuit telephone-line and the telephone thereof at the substation, of a return-circuit for the line connected with the central point of the winding of the substation-telephone, and an impedance-coil in the return-circuit, a bridge of the line-circuit at thecentral office, a signaling instrument associated with the line to respond to current therein, and a source of current in the return-circuit for operating the said signaling instrument, as described.

6. The combination with a telephone-line and a switch controlling the continuity of the line at the substation, of a relay and a source of current in the line at the central ofce, a spring-jack connected with the line, a plug for making connection with the spring-jack, a conductor attached thereto adapted to be brought into parallel circuit with the relay when connection is made with the line, a source of current in that conductor of proper strength and polarity to reduce the dierence of potential between the terminals of the relay to substantially zero, a supervisory-lamp signal in the conductor, a shunt about the signal and a source of current in the shunt adapted to reduce the dierence of potential about the supervisory lamp substantially to zero, while the line-circuit is complete, as described.

In witness whereof I hereunto subscribe my name this 3d day of October, A. D. 1896.

CHARLESV E. SCRIBNER.

Witnesses ELLA EDLER, PEARL CLENDENING.

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